In a conventional Otto cycle internal combustion engine, each cylinder performs four strokes per cycle—intake, compression, power, and exhaust. As a result, two revolutions of the engine's crankshaft are required for each power stroke.
By contrast, a split-cycle engine divides these four strokes between at least two paired cylinders—one for intake/compression and another for power/exhaust. In some split-cycle engine configurations compressed air is transferred from the compression cylinder to the power cylinder through a transfer or crossover passage. Fuel is subsequently injected and fired in the power cylinder to produce the power stroke.
Additionally, in some split-cycle engines, an expander cylinder is also provided to take advantage of the energy contained in post-combustion exhaust gases to create additional mechanical work by allowing further gas expansion. In such a case, after the power stroke, exhaust gases are transferred from the power cylinder to the piston expander via an exhaust port or passage, thereby displacing the expander cylinder.